(1) Field of the Invention
The present invention relates to miniature, highly sensitive undoped diamond single crystal and diamond thin film sensors. In particular, the diamond thin films are doped so as to be semi-conductive. The sensors are used to measure strain.
(2) Description of Related Art
Diamond piezoresistive sensors outperform their Si or SiC counterparts in sensitivity, especially in harsh environments and at high temperatures (Vaseashta, S. B. et al., Diamond--a novel sensing material, J. of Intelligent Material Systems and Structures 4 (1993) 129-135; Taher, I. et al., Piezoresistive microsensors using p-type CVD diamond films, Sensors and Actuators A 45 (1994) 35-43 and Aslam, M. et al., Piezoresistivity in vapor-deposited diamond films, Appl. Phys. Lett. 60 (23) (1992) 2923-2925). The reported piezoresistive gauge factors (GF) of single crystal and polycrystalline diamond are in the ranges of 500-3836 (most typically 2000-3836) (Taher, I. et al., Piezoresistive microsensors using p-type CVD diamond films, Sensors and Actuators A 45 (1994) 35-43) and 10-1000 (typically 10-100) (Taher, I. et al., Piezoresistive microsensors using p-type CVD diamond films, Sensors and Actuators A 45 (1994) 35-43; Aslam, M. et al., Piezoresistivity in vapor-deposited films, Appl. Phys. Lett. 60 (23) (1992) 2923-2925); Dorsch, O. et al., Piezoresistive effect in boron-doped diamond thin films, Diamond 92 (ICNDST-3), Heidelberg, Germany, September 1992, pp. 20.2-20.3; Wur, D. R. et al., Fabrication and characterization of doped polycrystalline diamond film (PDF) for strain sensing applications, in Proc. 7th Int. Conf. Solid State Sensors and Actuators (Transducers '93), Okohama, Japan Jun. 7-10, 1993, pp. 722-725 and Deguchi, M. et al., Piezoresistive property of CVD diamond films, presented at Diamond '96 (Diamond Films) jointly with ICNDST-5, Tours, France, September 8-13, Abstract No. 16.2, 1996 and Davidson, J. L. et al., Microelectronic pressure sensors with diamond piezoresistors on diamond diaphragm, Advances in New Diamond Science and Technology, 1994, pp. 693-700), respectively. As the chemical vapor deposited (CVD) polycrystalline diamond is inexpensive, it can become a commercially viable piezoresistive sensor material if its GF can rival that of single crystal diamond.
The patent art describe various sensing devices and diamond films. Included are U.S. Pat. No. 3,884,080 to Chapman; U.S. Pat. No. 4,492,123 to Reich; U.S. Pat. No. 4,806,900 to Fujimori et al; U.S. Pat. No. 5,081,438 to Nakahata et al; U.S. Pat. No. 5,089,802 to Yamazaki; U.S. Pat. No. 5,183,530 to Yamazaki; U.S. Pat. No. 5,298,749 to Inushima and U.S. Pat. No. 5,695,670 to Fujii et al. Doped diamond is a preferred material for thermistors.
Also of interest are U.S. Patent No. 3,433,684 to Zanowick et al; U.S. Pat. No. 4,808,009 to Sittler et al; U.S. Pat. No. 4,826,784 to Salerno et al; U.S. Pat. No. 4,863,529 to Imai et al; U.S. Pat. No. 4,919,974 to McCune et al; U.S. Pat. No. 4,925,701 to Jansen et al; U.S. Pat. No. 5,006,203 to Purdes; U.S. Pat. No. 5,066,938 to Kobashi et al; U.S. Pat. No. 5,075,094 to Morrish et al; U.S. Pat. No. 5,082,359 to Kirkpatrick; U.S. Pat. No. 5,082,522 to Purdes et al; U.S. Pat. No. 5,087,434 to Frenklach et al; U.S. Pat. No. 5,107,317 to Takasaki; U.S. Pat. No. 5,114,696 to Purdes; U.S. Pat. No. 5,110,577 to Tamor et al; U.S. Pat. No. 5,131,963 to Ravi; U.S. Pat. No. 5,144,380 to Kimoto et al; U.S. Pat. No. 5,173,761 to Dreifus et al; U.S. Pat. No. 5,186,973 to Garg et al; U.S. Pat. No. 5,190,823 to Anthony et al; U.S. Pat. No. 5,204,210 to Jansen et al; U.S. Pat. No. 5,242,711 to DeNatale et al; U.S. Pat. No. 5,260,141 to Tsai et al; U.S. Pat. No. 5,271,971 to Herb et al; U.S. Pat. No. 5,290,592 to Izuchi et al; U.S. Pat. No. 5,298,286 to Yang et al; U.S. Pat. No. 5,308,661 to Feng et al; U.S. Pat. No. 5,309,000 to Saito et al; U.S. Pat. No. 5,317,302 to Yamazaki; U.S. Pat. No. 5,334,342 to Harker et al; U.S. Pat. No. 5,474,808 to Aslam and U.S. Pat. No. 5,488,350 to Aslam et al.